Transport is a major component of economic activity in and of itself and as a factor input to most other economic activities. It has many effects on the environment: air pollution raises concern mainly in urban areas where road traffic and congestion are concentrated, though road transport also contributes to regional and global pollution problems such as acidification and climate change; vehicles present waste management issues; and transport infrastructure exerts pressures on the environment through use of space and physical transformation of the natural environment (e.g. fragmentation of natural habitats).
Road transport dominates compared to other transport modes. The volume of road traffic depends on the demand for transport (largely determined by economic activity and transport prices) and on transport supply (e.g. the development of road infrastructure).
The indicators presented here relate to:
Road traffic and vehicle intensities, i.e. traffic volumes per unit of GDP and per kilometre (km) of road, and vehicle numbers per capita and per kilometre of road.
Traffic volumes are expressed in billions of km travelled by road vehicles. Data refer to total km travelled on all roads on national territory by national vehicles, with the exception of two- and three-wheeled vehicles, caravans and trailers. They are usually estimates: the average number of km travelled each year by road vehicles is multiplied by the number of motor vehicles in use.
Road infrastructure densities, i.e. the length of road and motorway networks per km2 of land area. The data describe the situation on 31 December of each year.
The total road network includes all roads in a given area, i.e. motorways, main or national highways, secondary or regional roads, and others. Private roads are excluded.
Motorways are a class of roads differing from main or national, secondary or regional, and other roads, and characterised by not serving properties bordering on them.
The indicators should be read in connection with information on the modal split of transport and on the structure of the vehicle fleet. They should further be complemented with information on congestion rates and air pollution from road traffic.
Since 1990, countries' efforts in introducing cleaner vehicles have been offset by growth in vehicle numbers and the increased scale of their use. This resulted in additional fuel consumption, CO2 emissions and road building. Road traffic, both freight and passenger, is expected to increase further in a number of OECD countries.
GHG emissions from the transport sector increased until the latest recession. After falling from 2007, they were at about the same level in 2009 as in 2000.
In all OECD countries, private cars dominate the passenger transport mode, although there are notable differences in the modal shares. Since 1990, growth in private car use followed the same trend as GDP, but increased at a slightly lower rate.
Overall, transport activities remained coupled to GDP growth. In more than one-third of OECD countries, road traffic growth rates exceeded economic growth.
Traffic intensities per unit of GDP and vehicle availability per capita show wide variations among OECD countries:
Road density has progressed at a significantly slower pace than economic activity in most OECD countries, while the motorway density has rapidly increased, particularly in the last decade. Road density trends are similar for OECD Americas and OECD Europe, but the motorway density increased at a much higher rate in Europe, a fact perhaps related to the enlargement of the European Union (+17% between 2000 and 2008).
Indicators on road traffic need to be interpreted carefully; many underlying statistics are estimates. Data on vehicle stocks and road networks should exhibit a reasonably good level of comparability among countries and over time, with a few exceptions due to differences in the definition of roads and of goods vehicles across countries.